In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. One defect in prior formation techniques is caused when an air bubble is trapped between the forming roller and the polyethylene which will form the surface for casting of photosensitive materials. This air bubble will form a pit that will cause a defect in the photographic performance of photographic materials formed on the polyethylene. It would be desirable if a more reliable and improved surface could be formed at less expense.
In color papers there is a need for providing color papers with improved resistance to curl. Present color papers will curl during development and storage. Such curl is thought to be caused by the different properties of the layers of the color paper as it is subjected to the developing and drying processes. Humidity changes during storage of color photographs lead to curling. There are particular problems with color papers when they are subjected to extended high humidity storage such as at greater than 50% relative humidity. Extremely low humidity of less than 20% relative humidity also will cause photographic papers to curl.
In photographic papers the polyethylene layer also serves as a carrier layer for titanium dioxide and other whitener materials as well as tint materials. It would be desirable if the colorant materials rather than being dispersed throughout the polyethylene layer could be concentrated nearer the surface of the layer where they would be more effective photographically.
It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene in receiver sheets for thermal dye transfer.
A photographic paper commercially available has a single color printed logo or other brand information printed on the base paper that forms the back of the photographic element. This logo is covered by a layer of polyethylene. The present product is practically limited to a single color because the present production machines are limited by cost and space limitations to a single color press for printing the indicia onto the back of the base paper.
Other imaging materials also have substrates that are not easily provided with multicolor printing on the back of the substrate. This includes materials such as thermal dye transfer materials, electrophotographic, and ink jet substrate materials.
Problem to be Solved by the Invention
There is a need for a reliable, low cost, and high quality method of printing multicolor information and illustrations on the back of imaging materials, particularly color photographic paper.